1. Field of the Invention
The subject invention relates to an apparatus for efficiently locating a nerve and for subsequently delivering an anesthetic to the nerve.
2. Description of the Prior Art
Many medical procedures require a patient to be at least locally anesthetized. A regional anesthesia or nerve block offers advantages over general anesthesia for many medical procedures. For example, a regional anesthesia or nerve block typically is less traumatic to the patient undergoing surgery and often permits a shorter post-operative recovery.
A regional anesthesia or nerve block necessarily requires location of the nerve to which anesthetic agent will be administered. The prior art includes methods for locating the nerve. In most such prior art methods, the doctor typically uses general knowledge of physical anatomy to approximately locate the targeted nerve. In accordance with one prior art method, an electrically conductive pad is positioned on the skin on a portion of the patient's body at some distance from the targeted nerve. For example, if the targeted nerve is in the shoulder, the electrically conductive pad may be secured to a distal portion of the arm. The electrically conductive pad is connected by a wire to a prior art stimulator box that is capable of generating electrical current, as explained further herein. An electrically insulated needle cannula with an uninsulated conductive tip is then urged through the skin and subcutaneous tissue in the general direction of the nerve to be anesthetized. The prior art needle is connected by a wire to the prior art electrical stimulator box.
The prior art stimulator box is electrically powered and is operative to produce an adjustable current pulse for a duration of approximately 100-200 microseconds (".mu.S"). The current pulse is set initially to a level of approximately 1.0-5.0 milliamps ("mA"). This current level typically is sufficient to stimulate the targeted nerve when the needle has been placed into the tissue in the approximate area of the targeted nerve. The stimulation will cause a noticeable muscle twitch on areas of the body controlled by the targeted nerve (e.g., the fingers). The current then is decreased slowly until the twitching disappears. The prior art needle then is advanced slowly toward the targeted nerve until the twitching reappears. This iterative procedure continues until the prior art needle is able to generate noticeable muscle twitches at a current level of approximately 0.2-0.3 milliamps. At this point, the prior art needle is considered to be sufficiently close to the targeted nerve for administration of the anesthetic agent. The anesthetic agent then is delivered directly through the needle while the needle continues to produce the current pulses. Cessation of the muscle twitch typically is considered to indicate successful location of the nerve.
The prior art electrolocation procedure is intended to ensure accurate placement of a needle for delivery of anesthetic. However, the prior art device and the prior art procedure for electrolocation of a targeted nerve have several drawbacks. For example, the prior art electrolocation device, including the stimulator box, is a fairly large, costly and reusable piece of equipment that is not easily sterilized. Thus, there are problems with using the prior art electrolocation device in the sterile environment of an operating room. It is typically necessary to employ two technicians for carrying out this prior art procedure, namely a first technician operating under sterile conditions and manipulating the needle, and a second technician spaced from the first technician and operating under non-sterile conditions to incrementally decrease the current level. The use of two technicians necessarily requires fairly high costs and requires considerable coordination and communication between the two technicians.
Second, the prior art electrolocation device does not provide a definitive indication of when the needle is properly positioned for injecting the anesthetic. The attending physician must rely upon judgment and experience to determine when the needle is in the optimum position.
Third, the considerable distance between the insulated needle and the prior art conductive pad requires the generation of a relatively high voltage to achieve the desired current level. A voltage of at least 25 volts ("V") is common in the prior art electrolocation apparatus. These relatively high voltage levels limit the use of the prior art apparatus. For example, the high voltage levels can affect the performance of pacemakers and other implanted electronic devices. Hence, the prior art electrolocation device generally cannot be used on patients with implanted electronics.
Additionally, the relatively high energy creates the risk of arcing. Hence the prior art electrolocation apparatus cannot be employed in many surgical environments, such as those where oxygen is being used, due to the risk of fire or explosion. The high current levels may also create the potential for tissue damage in proximity to the needle.